1. Field of the Invention
The present invention relates to an integrated circuit device. More particularly, the present invention relates to a method of forming a contact and a semiconductor device.
2. Description of Related Art
During the development of integrated circuit devices, it has been shown that devices can achieve high speed operation and low electrical consumption through the reduction of the device dimensions. However, the technology in miniaturizing device dimension has approached a technical bottleneck. Further, due to reasons like higher cost, other technology asides from the technology in miniaturizing device dimension, needs to be developed to improve the drive current. People skilled in the art have proposed controlling the stress at the channel region of the transistor to overcome the restraint in size reduction of devices. This method relies on stress to alter the distance of the silicon lattice to enhance the mobility of electrons and holes in order to enhance the efficiency of devices.
One method to enhance the efficiency of devices via the stress control method is the application a silicon nitride layer as a contact etch stop layer to generate stress. The drive current of the device is thereby increased to enhance the efficiency of devices. However, other problems still exist in the abovementioned method in which the efficiency of devices is adversely affected.
FIGS. 1A to 1E are schematic, cross-sectional views showing the steps for fabricating a contact according to the prior art.
Referring to FIG. 1A, a plurality of metal oxide semiconductor devices 102 is formed on a substrate 100. A gap 104 is present between every two metal oxide semiconductor devices 102.
Referring to FIG. 1B, a silicon nitride layer 106 is formed over the substrate 100 as a stress layer, wherein the silicon nitride layer 106 covers the entire substrate 100 and the metal oxide semiconductor devices 102. The thickness of the silicon nitride layer 106 is highly related to its stress value. In other words, the thicker the silicon nitride layer 106, the higher its stress value. However, when a thicker silicon nitride film layer is formed to enhance the device efficiency, seam is generated in the silicon nitride layer 106 inside the gap 104. The reliability of the subsequent process is seriously affected. More particularly, when the level of device integration increases, the gap 104 becomes narrower. Seam and void are even more easily generated in the silicon nitride layer 106.
Referring to FIG. 1C, a dielectric layer 110 is formed above the silicon nitride layer 106. Since seam is formed in the silicon nitride layer 106, the dielectric layer 110 fails to cover the silicon nitride layer 106 completely. Only a portion of the seam 108 is filled with the dielectric layer 110. As shown in the picture taken by transmission electron microscopy as shown in FIG. 2, at the region depicted by the reference number 200, the seam 108 in the silicon nitride layer 106 is not completely filled with the dielectric layer 110.
Thereafter, as shown in FIG. 1D, an etching process is performed to form a contact in the dielectric layer 110 and the silicon nitride layer 106. Due to the presence of seam 108 in the silicon nitride layer 106, after the etching of the dielectric layer 110 and the silicon nitride layer 106, residues 112 are formed at the bottom of the contact opening 114 as shown by the reference number 300 in the picture taken by transmission electron microscopy in FIG. 3.
Continuing to FIG. 1E, the contact opening 114 is then filled with a metal material to form a contact 116. The residues 112 at the bottom of the contact opening 114 increase the resistance of the contact 116. A short circuit may even generate between the contact 116 and the metal oxide semiconductor device 102 to affect the reliability and efficiency of the device.
Accordingly, the development of a technology that can apply a silicon nitride layer to generate stress to increase the device efficiency, while the generation of defects in the film layer is obviated during the fabrication of the silicon nitride layer is urgently in demand.